"There is no room for callousness, non-conformance to community and police standards, nor brutality in policing today," Chief Lowe said. "He was callous, non-conforming and brutal in his treatment of Brandy Martin."

Mr. McDonald, 33, who was a police officer for 12 years, had been on unpaid leave.

He had said he gave Brandy Martin, 17, a $20 bill to pay for his food Feb. 17 at a Wendy's restaurant drive-through window. She said it was a $10 bill.

Mr. McDonald walked into the restaurant and confronted Ms. Martin and the two argued. Mr. McDonald used the pepper spray on Ms. Martin when she refused to leave with him after he arrested her. The confrontation was caught on the restaurant's surveillance camera.

The spray contains cayenne pepper that can make the eyes water and cause coughing. It is designed to temporarily incapacitate someone and does not cause permanent injury.

Mr. McDonald could not be located for a response Friday. His lawyer, Robert Caspar Jr., did not return calls to his office. An office aide said Mr. Caspar had not seen the police report on the internal investigation of Mr. McDonald.

The officer was found innocent of assault charges last month after a visiting Municipal Court judge ruled he had enough reason to arrest Ms. Martin.

Civil rights activist Jessie Gooding had urged police to fire Mr. McDonald. Mr. Gooding noted that a Dayton Daily News report said Mr. McDonald believes he may have mistakenly accused the teen-ager. Mr. McDonald is white and the worker is black.

"The officer is saying now he might not have had the $20. That's a blatant distortion," said Mr. Gooding, president of the Dayton branch of the National Association for the Advancement of Colored People.

Mr. McDonald had testified he was certain he paid with a $20 bill because he had two bills in his pocket and the other was a $5 bill. After a police hearing Tuesday, Sgt. Glenn Miller, an internal affairs investigator, said he couldn't justify Ms. Martin's arrest because no one established that a theft had been committed.